[Milsurplus] Fwd: Re: Lowering Receiver B+, Again.

[Mike Feher]

As I recall, lowering filament voltage on a tube is not such a good idea.
While the filament may last longer, some sort of contamination takes place,
maybe between filament and cathode, I do not recall what or the physics,
rendering the tube useless much quicker. Also, reducing the B+ substantially
could have an effect on the electrolytics in the radio which do have a
memory associated with them. This would only be a problem if the radio was
ever attempted to run again on its rated voltage. Merry Christmas & HNY & 73
- Mike  

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
848-245-9115

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
Kenneth G. Gordon
Sent: Thursday, December 22, 2016 11:33 AM
To: Milsurplus at mailman.qth.net >> Milsurplus
Subject: Re: [Milsurplus] Fwd: Re: Lowering Receiver B+, Again.

I'm with Bruce on this one, David:

1) Full-wave rectification.

2) CHOKE input (get rid of the input capacitor). You MAY have to increase
the capacitance of the remaining capacitor(s) to keep ripple at a low level,
though.

3) Bucking transformer on the input.

Reducing the filament voltage is not going to effect operation and will
contribute to longevity of the tubes.

You might also consider inserting a resistor in the B+ feed, since the
current draw in receivers is normally pretty constant.

On another note: reducing receiver operating voltages appears to have almost
no effect on operation of the receiver at all.

I have mentioned this a time or two before, but I think repeating it may
contribute to the ongoing discussion:

Many years ago, I read an article in one of our ham magazines in which the
author recounted his experiences with reducing the operating voltages in a
Drake 2B receiver. To make a long story shorter, he reduced the operating
voltages in steps to something like 12VDC from the normal 250 VDC, and found
that other than it taking a bit longer for his receiver to warm up, and the
reduction in audio output power,  nothing else was effected.

He finally raised it back up to about 50 volts, mainly in the interests of
adequate audio output power, and left it there.

The main effect in the operations which he noted was very noticeable
reduction in noise, so much so that signals seemed to "pop out" at him when
he tuned across them.

In my own experiments, I have determined that the optimum (in my opinion)
for operating voltages for our ARC-5 receivers is about 170 VDC, although at
that voltage, one must move the screen voltage feed to the "hot" end of the
divider string.

BTW, the HFO in the ARC-5s at the normal 250 VDC input is operating at a
voltage of 35 VDC. It seems to have plenty of injection to the mixer at a
voltage of as low as 12 VDC, so I really don't think reduction in operating
voltage is going to effect your RME in that regard either.

In any case, in my opinion, 340 VDC is MUCH too high for a receiver!!! It is
not necessary.

Ken W7EKB

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